The present invention is directed to ink compositions. More specifically, the present invention is directed to aqueous ink compositions that are particularly suitable for use in ink jet printing processes. One embodiment of the present invention is directed to an ink composition which comprises an aqueous liquid vehicle, a dye, and a cyclodextrin.
Ink jet printing systems generally are of two types: continuous stream and drop-on-demand. In continuous stream ink jet systems, ink is emitted in a continuous stream under pressure through at least one orifice or nozzle. The stream is perturbed, causing it to break up into droplets at a fixed distance from the orifice. At the break-up point, the droplets are charged in accordance with digital data signals and passed through an electrostatic field which adjusts the trajectory of each droplet in order to direct it to a gutter for recirculation or a specific location on a recording medium. In drop-on-demand systems, a droplet is expelled from an orifice directly to a position on a recording medium in accordance with digital data signals. A droplet is not formed or expelled unless it is to be placed on the recording medium.
Since drop-on-demand systems require no ink recovery, charging, or deflection, the system is much simpler than the continuous stream type. There are two types of drop-on-demand ink jet systems. One type of drop-on-demand system has as its major components an ink filled channel or passageway having a nozzle on one end and a piezoelectric transducer near the other end to produce pressure pulses. The relatively large size of the transducer prevents close spacing of the nozzles necessary for high resolution printing, and physical limitations of the transducer result in low ink drop velocity. Low drop velocity seriously diminishes tolerances for drop velocity variation and directionality, thus impacting the system's ability to produce high quality copies, and also decreases printing speed. Drop-on-demand systems which use piezoelectric devices to expel the droplets also suffer the disadvantage of a slow printing speed.
The other type of drop-on-demand system is known as thermal ink jet, or bubble jet, and produces high velocity droplets and allows very close spacing of nozzles. The major components of this type of drop-on-demand system are an ink filled channel having a nozzle on one end and a heat generating resistor near the nozzle. Printing signals representing digital information originate an electric current pulse in a resistive layer within each ink passageway near the orifice or nozzle, causing the ink in the immediate vicinity to evaporate almost instantaneously and create a bubble. The ink at the orifice is forced out as a propelled droplet as the bubble expands. When the hydrodynamic motion of the ink stops, the process is ready to start all over again. With the introduction of a droplet ejection system based upon thermally generated bubbles, commonly referred to as the "bubble jet" system, the drop-on-demand ink jet printers provide simpler, lower cost devices than their continuous stream counterparts, and yet have substantially the same high speed printing capability.
The operating sequence of the bubble jet system begins with a current pulse through the resistive layer in the ink filled channel, the resistive layer being in close proximity to the orifice or nozzle for that channel. Heat is transferred from the resistor to the ink. The ink becomes superheated far above its normal boiling point, and for water based ink, finally reaches the critical temperature for bubble formation or nucleation of around 280.degree. C. Once nucleated, the bubble or water vapor thermally isolates the ink from the heater and no further heat can be applied to the ink. This bubble expands until all the heat stored in the ink in excess of the normal boiling point diffuses away or is used to convert liquid to vapor, which removes heat due to heat of vaporization. The expansion of the bubble forces a droplet of ink out of the nozzle, and once the excess heat is removed, the bubble collapses on the resistor. At this point, the resistor is no longer being heated because the current pulse has passed and, concurrently with the bubble collapse, the droplet is propelled at a high rate of speed in a direction towards a recording medium. The resistive layer encounters a severe cavitational force by the collapse of the bubble, which tends to erode it. Subsequently, the ink channel refills by capillary action. This entire bubble formation and collapse sequence occurs in about 10 microseconds. The channel can be refired after 100 to 500 microseconds minimum dwell time to enable the channel to be refilled and to enable the dynamic refilling factors to become somewhat dampened. Thermal ink jet processes are well known and are described in, for example, U.S. Pat. No. 4,601,777, U.S. Pat. No. 4,251,824, U.S. Pat. No. 4,410,899, U.S. Pat. No. 4,412,224, and U.S. Pat. No. 4,532,530, the disclosures of each of which are totally incorporated herein by reference.
U.S. Pat. No. 90,417 (Zengeler) discloses a dry powder ink containing dextrine, British gum, roasted starch, gum-arabic, or any other soluble gum or mucilaginous substance in combination with a mixture of aniline or any of its salts or compounds with oxidizing agents of any kind, such as chlorate or bichromate of potassa, sulfate, acetate, or chloride of copper, or the like. The dry powder produces a black indelible stain or dye, irremovable by acids or alkalies, when the compound is mixed or diluted with water and applied to absorbent or adherent surfaces or substances.
U.S. Pat. No. 1,325,971 (Akashi) discloses a solid ink comprising a mixture of a dye with dextrin, soluble gum tragacanth, thymol, and lactic acid, the mixture being sufficiently kneaded together by the addition of a small quantity of water so as to produce a plastic or pasty substance. When put into water, the composition gives at once a liquid ink clearly colored corresponding to the coloring material employed.
U.S. Pat. No. 1,404,355 (Evans et al.) discloses a printing ink which is a mixture of a viscous liquid comprising by weight at least 40 percent of a polyhydric alcohol of the saturated series and a relatively small amount of a solution of a film-forming material, together with a solid drying agent. Examples of water solutions of film-forming materials include glue, gum arabic, cherry gum, dextrine, and starch.
U.S. Pat. No. 1,479,533 (Cooney) discloses an ink in the form of paste comprising water, white potato dextrin, gallic acid, ferrous sulfate, hydrochloric acid, carbolic acid, glycerine, and coloring matter. The ink paste is rendered fluid for use by the addition of water, providing a writing fluid free of suspended matter.
U.S. Pat. No. 1,607,060 (Dean) discloses a glossy water color ink composition prepared by admixing water with a solution comprising gum arabic soap, starch, dextrine, a tar product adapted to prevent the mixture from souring, glucose, and water.
U.S. Pat. No. 2,684,303 (Leonard et al.) discloses a high reflectance quick drying marking ink suitable for inscribing on glass and clear solid plastic surfaces which comprises a dispersion of from about 18 to about 22 percent by weight titanium dioxide in a water solution of from about 7 to about 10 percent by weight dextrin in which the weight ratio of titanium dioxide to dextrin is between about 21/4 and about 23/4 to 1, the dispersion being thickened with from about 0.2 to about 0.4 percent by weight gum tragacanth and with from about 0.9 to about 1.1 percent by weight bentonite, and further containing from about 1.5 to about 2.5 percent by weight diethylene glycol monomethyl ether and a small amount of a microbicide and of a wetting agent.
U.S. Pat. No. 3,361,582 (Lewis) discloses a base vehicle for water content water color printing inks containing sodium caseinate, tapioca dextrine, sulfonated castor oil, water, glycerine, formaldehyde solution, ammonium hydroxide, urea, and hydrated lime.
Although known compositions are suitable for their intended uses, a need continues to exist for ink compositions suitable for use in ink jet printing processes. In addition, a need remains for ink compositions particularly suitable for thermal ink jet printing processes. Further, there is a need for ink compositions that exhibit rapid drying times. There is also a need for ink compositions that have aqueous liquid vehicles and contain oil soluble or alcohol soluble dyes. Additionally, there is a need for ink compositions with aqueous liquid vehicles that exhibit improved waterfastness compared to aqueous inks containing water soluble dyes.